Introduction to lithium battery protection board
Lithium battery protection board is the charge and discharge protection for the series lithium battery pack; when fully charged, it can ensure that the voltage difference between each unit battery is less than the set value (generally ±20mV), and realize the equalization of each unit of the battery pack. , effectively improving the charging effect in the series charging mode; simultaneously detecting the overvoltage, undervoltage, overcurrent, short circuit, and overtemperature conditions of each single cell in the battery pack, protecting and extending the battery life; undervoltage protection enables each A single battery prevents damage to the battery due to overdischarge during discharge.
Lithium battery protection board ’s working principle
The working principle of the protection board:
As is shown in the figure, the IC is powered by the battery, and the voltage can guarantee reliable operation at 2v-5v.
1. Overcharge protection and overcharge protection recovery
When the battery is charged so that the voltage exceeds the set value VC (4.25-4.35V), VD1 flips to make Cout low, T1 is off, and charging stops. When the battery voltage falls back to VCR (3.8-4.1V, the specific overcharge protection recovery voltage depends on the IC), Cout goes high, T1 turns on charging continues, VCR must be less than VC fixed value to prevent frequent jumps .
2. Over-discharge protection and over-discharge protection recovery
When the battery voltage drops to the set value VD (2.3-2.5V, the specific overcharge protection voltage depends on the IC) due to discharge, VD2 flips, after a short time delay, Dout becomes low level, T2 is cut off. The discharge stops and when the battery is placed in charge, the internal OR door is flipped and T2 is turned back on to prepare for the next discharge.
3. Overcurrent, short circuit protection
When the circuit charge and discharge loop current exceeds the set value or is short-circuited, the short-circuit detection circuit operates to turn off the MOS transistor and the current is cut off.
Lithium battery protection board’s Common malfunctions
1. no display, low output voltage, can not afford the load
2. no charging
3. no internal resistance, large internal resistance
4. no resistance
6. not decoding
Lithium battery protection board detection
1. ensure that the sampling line (wire) is connected correctly.
Take 7-string battery 8pin line as an example
B-line connected battery total negative
B1 line connected to the first string of battery positive
B2 line connected to the second string of battery positive
B3 line connected to the third string battery positive
B4 line connected to the 4th string battery positive
B5 line connected to the fifth string battery positive
B6 line connected to the sixth string battery positive
B7 line connected to the 7th string battery positive
PS: The 7th string of the 7th string of the battery positive pole is also the total positive pole, the same can be analogized to any string battery pack.
2. through the multimeter to determine the correct wiring of the battery cable
(1) Press the B-line terminal and the multimeter red test lead B1 line terminal with the black pen of the multimeter to obtain the first series battery voltage is 3.584V.
(2) By pressing the B1 line terminal with the multimeter black test pen and the red table pen pressure letter B2 line terminal of the multimeter, the second series battery voltage is 3.584V.
(3) Measuring by this method, it is concluded that:
The first string battery voltage: 3.584V
The second string battery voltage: 3.584V
The third string battery voltage: 3.585V
The fourth string battery voltage: 3.585V
The fifth string battery voltage: 3.583V
The sixth string battery voltage: 3.583V
The seventh string battery voltage: 3.584V
The 7-string voltage is 3.58V, the wiring is correct, and the battery voltage difference is less than 0.002V, and the battery consistency is good. PS: The voltage per string of the battery should be: ternary lithium voltage is 3.0-4.2V; lithium iron phosphate voltage is 2.0-3.6V; lithium titanate is about 1.5-2.75V. If any string of voltages differs by more than 2V, it indicates that the cable is connected incorrectly and needs to be rewired.
3. After the measurement voltage is normal, plug the cable into the protection board and measure the resistance between the protection board B- and P-. The resistance is 0, which means that they are unobstructed before, and the protection board is good.
4. Alternatively, by connecting the B-line, measure the voltage of B- and the total positive pole of the battery and the voltage of P- and the total positive pole of the battery. The voltage is the same, indicating that the protection board is normal (the protection board is equivalent to the switch, the switch is already open, and the current can be safely passed). The example test is: B-to the battery total positive voltage is 25.11VP-to the battery total positive voltage is 25.11V. The two voltages are consistent to indicate that the protection board is normal. If P- discharges through a large current, there will be a slight pressure drop, and the protection plate will heat up (about 50 degrees), which is a normal phenomenon.
Precautions for testing lithium battery protection board
1. When the voltage is measured, the meter is placed correctly. When it is touched, it will short-circuit and smoke.
2. When connecting the protection board, be sure to connect the cable first and then insert the protection board. Inserting the protection board may cause the board to burn out.